Method for diagnosis of a volume flow control valve in an internal combustion engine comprising a high-pressure accumulator injection system

ABSTRACT

The invention relates to an internal combustion engine comprising a high-pressure accumulator injection system wherein the swept volume and the pressure are regulated by means of a volume flow control valve (VCV) and a pressure control valve (PCV). The inventive method consists in checking, during the overrun condition of the internal combustion engine, whether predetermined release conditions for carrying out the diagnosis are fulfilled, and in the event of a positive result, the control valve (VCV) is closed for a predetermined period of time (t 1 ). During said period (t 1 ), values relating to fuel pressure (FUP) are detected by means of the pressure sensor ( 21 ) and compared with a predetermined threshold value (FUP-SW), the control valve (VCV) being deemed faultless if said fuel pressure (FUP) values are sufficiently often below the threshold value (FUP_SW) during the cited period of time (t 1 ).

DESCRIPTION

Method for diagnosis of a volume flow control valve in an internalcombustion engine comprising a high-pressure accumulator injectionsystem

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The invention relates to a method for diagnosis of a volume flow controlvalve in an internal combustion engine comprising a high-pressureaccumulator injection system. Fuel is delivered by a pre-feed pump and ahigh-pressure pump to a high-pressure accumulator to which at least oneinjector for injecting the fuel into at least one cylinder of theinternal combustion engine is connected, with a pressure sensor assignedto the high-pressure accumulator and of a pressure regulation controlvalve for setting the pressure in the high-pressure accumulator on thebasis of the fuel pressure signal delivered by the pressure sensor.

High-pressure accumulator injection systems are increasingly being usedfor supplying fuel to internal combustion engines. Such injectionsystems are known as common-rail systems for diesel engines and as HPDI(High Pressure Direct Injection) systems for gasoline engines. Theseinjection systems feature components such as a pre-feed pump,high-pressure pump, fuel filter, pressure control valve, volume flowcontrol valve, high-pressure accumulator, injectors (injection valves)and associated lines.

The pre-feed pump delivers fuel from a fuel storage tank via the fuelfilter to the high-pressure pump. This compresses the fuel and feeds itunder high pressure into the high-pressure accumulator (common rail),from where the injectors on the individual cylinders are supplied. Theopening and closing of the injectors is generally controlledelectrically or electromagnetically.

As well as for pressurized storage, the high-pressure accumulator isalso used to smooth out pressure pulses, for which a sufficiently largestorage volume is necessary.

The volume flow control valve is used for demand-dependent setting ofthe volume flow of the high-pressure pump. With the aid of the pressurecontrol valve the pressure in the high-pressure accumulator is set inaccordance with the operating conditions of the internal combustionengine.

In addition to the electrical diagnosis of components of such ahigh-pressure accumulator injection system, plausibility checking isalso an important instrument for detecting operational faults. Inparticular pressure variations can occur in the high-pressureaccumulator in the above system if the volume flow control valve is notworking correctly. This can adversely affect driving characteristics andlead to higher exhaust gas emissions.

The occurrence of pressure oscillations can have causes other than avolume flow control valve which is not working correctly and istherefore not uniquely attributable to a defective volume flow controlvalve.

SUMMARY OF THE INVENTION

The object of the invention is to specify a method by which a defectivevolume flow control valve can be easily detected during the operation ofthe internal combustion engine.

This object is achieved by the features of Patent Claim 1.

For an internal combustion engine with a high-pressure accumulatorinjection system, in which the swept volume and the pressure are set bymeans of a volume flow control valve and a pressure control valve, acheck is made during the overrun condition of the internal combustionengine as to whether predetermined release conditions for performing thediagnosis are fulfilled, and if the result of the check is positive, thepressure control valve is closed for a predetermined length of time(diagnostic time). During the diagnostic period values for the fuelpressure are detected by means of the pressure sensor on thehigh-pressure accumulator and these values are compared withpredetermined threshold value for the fuel pressure. The control valveis classified as fault free if the values for the fuel pressure withinthe diagnostic period are below the threshold value sufficiently often.

It is especially advantageous for the pressure control valve to be ableto be opened briefly at the same time that the volume flow control valveis being closed. This achieves a rapid and defined pressure reduction.

Advantageously one or more of the following parameters are evaluated asrelease conditions for diagnosis:

In particular an inquiry is made as to whether the fuel-injection isswitched off (overrun mode), the speed of the internal combustion enginelies above a predetermined threshold value and the speed of the vehiclelies above a predetermined

threshold value, the clutch is engaged and there is no request from thedriver. To this end the signals from various sensors and generators areevaluated.

In order not to falsify the diagnosis the diagnosis is abortedimmediately if during the diagnosis period one of the release conditionsis no longer fulfilled.

Furthermore it is possible for the diagnosis to only be performed onceper driving cycle or at predetermined intervals respectively, providedthe activation conditions were fulfilled for a sufficient length oftime.

Further advantageous embodiments of the method in accordance with theinvention are specified in the subclaims.

The invention is explained in greater detail below with reference to thedrawing. The drawing shows:

BRIDF DESCRIPTION OF THE DRAWING

FIG. 1 a schematic diagram of an injection system for an internalcombustion engine operating with the direct fuel injection,

FIG. 2 A flowchart of the method in accordance with the invention and

FIG. 3 a diagram for selected signal curves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic diagram of the structure of a fuel-injectionsystem for an internal combustion engine BKM operating with direct fuelinjection, as is used under the name of common rail system above all invehicles with diesel engines. In this diagram only those components areshown which are needed for the understanding of the invention.

With this injection system fuel is drawn out of a fuel storage tank 10via a fuel line 11 through a pre-feed pump 12. The pre-feed pump 12delivers the fuel via a fuel filter 13 to a high-pressure pump 14 whichcompresses the fuel and feeds it under high pressure into ahigh-pressure accumulator 15 known as the rail. This high-pressureaccumulator 15, in addition to storing the fuel under pressure, also hasthe important task of smoothing out pressure variations by asufficiently high storage volume.

To enable the volume flow of the high-pressure pump 14 to be set in thehigh-pressure accumulator 15 in accordance with the relevant operatingconditions of the internal combustion engine BKM according to demand, anadditional throttle valve, referred to below as the volume flow controlvalve VCV, is arranged in the fuel line 11 between the pre-feed pump 12and the high-pressure pump 14. With the aid of this valve the deliveryflow of the high-pressure pump 14 can be controlled. This volume flowcontrol valve VCV is controlled by a control unit 16 via a control line17. The control unit 16 is a preferably integrated into an electroniccontrol device 18 of the internal combustion engine which controlsand/or regulates all the execution sequences needed to operate theinternal combustion engine BKM. To this end a plurality of input signalsES recorded by means of the corresponding sensors are fed to the controldevice 18 of the internal combustion engine BKM. Via output signal ASthe individual actuators and components are activated which arenecessary for the operation of the internal combustion engine BKM. Thecontrol unit 16 features a timer 32 as well as a memory 31 in whichvarious threshold values FUP SW, N _SW, VIST SW and times t1, t2 arestored for which the meaning will be explained in greater detail belowwith reference to the description of FIGS. 2 and 3. Furthermore an errormemory 36 is assigned to the control unit 16 and the control device 18.

To enable the pressure in the high-pressure accumulator 15 to be set inaccordance with the desired operating conditions of the internalcombustion engine BKM, a pressure control valve PCV is also connectedinto the fuel line 11 after the high-pressure pump 14. This pressurecontrol valve PCV controls and/or regulates excess fuel returned to thefuel storage tank 10 via a fuel return line 19 shown by a dashed line inthe diagram which would not be needed to maintain the desired pressurein the high-pressure accumulator 15, with the holding pressure of thepressure control valve PCV being set by the control unit 16 via acontrol line 20. A pressure sensor 21 is also provided for controllingthe pressure in the high-pressure accumulator 15. This pressure sensor21 is used to detect the fuel pressure FUP currently obtaining in thehigh-pressure accumulator 15 on the basis of which the control unit 16,in accordance with the desired operating conditions of the internalcombustion engine BKM, controls the pressure via the pressure controlvalve PCV.

Fuel pressures of between 0 and 1650 bar can be set in the high-pressureaccumulator 15 the aid of the arrangement shown. These fuel pressuresobtain over fuel injection lines 22 at injectors 23 (injection valves)which directly inject fuel into the combustion chambers of the internalcombustion engine BKM on demand. These injectors 23 generally feature aninjection nozzle connected to a needle under spring pressure. Theinjection process is initiated by the control unit 16 which is connectedvia control lines 24 to the injectors 23. The leakage flow occurring inthe injectors 23 is directed via fuel return lines 25 shown as dashedlines in the diagram into the fuel storage tank 10.

An engine speed sensor 28 is also provided on the internal combustionengine BKM which sends a signal corresponding to the revolutions N ofthe crankshaft of the internal combustion engine to the control unit 16for further processing. The signal VIST of a speed sensor 34, as well asthe signal of a pedal sensor module 35 are also fed to the controldevice 18. The latter is used to transfer the driver's wishes.

The pre-feed pump 12 is driven in a preferred embodiment via an electricmotor 26 which is connected via a control line 27 to the control unit16. Furthermore this type of electrically driven pre-feed pump 12 canalso be designed so that its speed can be regulated.

The pre-feed pump 12 and the high-pressure pump 14 can also be driven bythe internal combustion engine BKM and the speeds of the pumps are thenset with a fixed transmission ratio proportional to the speed of theinternal combustion engine. The pre-feed pump 12 is here preferablyintegrated into the housing of the high-pressure pump 14.

Furthermore it is also possible to drive the high-pressure pump 14independently of the speed of the internal combustion engine BKM, forexample by means of an electric motor.

When the internal combustion engine BKM is switched off, the pressurecontrol valve PCV is opened in order to let the fuel out of thehigh-pressure accumulator. The volume flow control valve VCV remainsopen for a short time after the internal combustion engine BKM is turnedoff during the re setting of the control unit 16 to refill the pumpchamber of the high pressure pump 14. Thus,

the next time that the internal combustion engine BKM is started, thefilling of this dead space is dispensed with, which leads to thehigh-pressure accumulator injection system being ready for operationmore quickly.

in a preferred embodiment the pressure control valve PCV is open withzero current, i.e. when the internal combustion engine BKM is switchedoff it is isolated. The volume flow control valve VCV is closed withzero current so that after expiry of the reset time by switching off thepower supply the fuel feed line 11 to the high-pressure pump 14 isinterrupted If the power supply fails both valves thus assume a safestate.

The flowchart shown in FIG. 2 and the timing diagram of selected signalsshown in FIG. 3 are used to illustrate how the volume flow control valveVCV can be tested to see whether it is functioning correctly. In thediagram according to FIG. 3 from top to bottom, the relevant curves overtime t for the fuel pressure FUP, the ON/OFF state of the volume flowcontrol valve VCV and of the pressure control valve PCV and also thestate of the flags LV CDN are plotted.

In a first procedural step S1 a check is made as to whether the internalcombustion engine BKM is in the overrun mode (fuel injection switchedoff, overrun cutoff), that is in a load state in which negative work isbeing done, meaning that the internal combustion engine is not doingwork but is consuming it. If an overrun condition does not obtain in theinternal combustion engine, the inquiry in procedural step S1 isnegative, so that no checking routine for the volume flow control valveVCV is started and this inquiry is executed repeatedly. Else, in aprocedural step S2, a check is made as to whether further releaseconditions for checking the volume flow control valve VCV are fulfilled.In particular an inquiry is made about whether the speed N of theinternal combustion engine is above a predetermined threshold value N_SWthe speed of the vehicle VIST is above a predetermined threshold valueVIST SW, the clutch 100 is engaged and the driver is not making anyrequests. This involves evaluation of signals such as those of sensors34 and of the pedal sensor module 35.

If one of the conditions is not fulfilled, a flag (marker) LV CDN=0 isset and the procedure is ended (procedural step S10). If however theseconditions are fulfilled, in a procedural step S3 the flag LV CDN=1 isset, and via corresponding signals the volume flow control valve VCV isclosed at starting time TSTART for a predetermined time t1 (diagnostictime). To achieve a rapid and defined pressure reduction in theinjection system, the pressure control valve PCV is opened for apredetermined time t2<t1 simultaneously with time TSTART. This latterstep is not absolutely necessary, but makes diagnosis more definite.After time t2 has elapsed the pressure control valve PCV is activatedagain and thereby a specific holding pressure set. The holding pressureis selected for example as a function of the speed N of the internalcombustion engine. The volume flow control valve VCV however remainsclosed.

The times t1, t2 are determined experimentally through trials and arestored in the memory 31 of control unit 16. These times t1, t2 arecontrolled and monitored by timer 32.

Measurements of the fuel pressure FUP now allow assessment of whetherthe volume flow control valve VCV can be activated.

Immediately after the closure of the volume flow control valve VCV thefuel pressure FUP drops very quickly. During the time t1 the fuelpressure FUP is constantly recorded by means of the pressure sensor 21(procedural step S4) and compared to a predetermined threshold value FUPSW (procedural step S5). If the fuel pressure FUP remains within thetime t1 sufficiently often below the threshold value FUP SW, in aprocedural step S6 the volume flow control valve VCV is classified asfault-free, else as defective (procedural step S7) and a correspondingentry is made in the fault memory 36 (procedural step S8). At the sametime the result, at least in the case of a faulty volume flow controlvalve VCV, can be indicated to the driver audibly and/or visually. Theinquiry about the fuel pressure FUP in the rail 15 by means of thepressure sensor 21 is appropriately filtered to exclude anydisturbances.

After the complete diagnosis sequence (time TENDE) the volume flowcontrol valve VCV will be opened again by means of signals of thecontrol unit 16 (procedural step S9). The degree of opening can in thiscase preferably be selected as a function of the speed N of the internalcombustion engine BKM. The procedure is then ended (procedural stepS10).

If during diagnosis the flag changes to LV CDN=0, for example caused bya request from the driver and recorded by the pedal sensor module 35,this leads to the diagnosis being aborted immediately. In this case anypressure variations which might occur could falsify the result of thediagnosis.

In addition it is also possible, to only allow the diagnosis to beperformed completely once per driving cycle or at specific intervals,provided the activation conditions were fulfilled for a sufficientlength of time.

1. A method for diagnosis of a fuel volume control valve for setting a fuel volume flow in an internal combustion engine, the method which comprises: providing a fuel system with a pre-feed pump, a high-pressure pump for feeding fuel to a high-pressure accumulator, a fuel control valve for setting a volumetric flow of the fuel fed by the high-pressure pump to the high-pressure accumulator, at least one injector for injecting the fuel into at least one cylinder of the internal combustion engine connected to the high-pressure accumulator, a pressure sensor assigned to the high-pressure accumulator, and a pressure control valve for setting a pressure in the high-pressure accumulator based on a fuel pressure signal from the pressure sensor; in overrun mode of the internal combustion engine, performing a check whether release conditions for executing the diagnosis are fulfilled, the release conditions selected from a group consisting of whether a speed of the internal combustion engine lies above a first predetermined threshold value, whether a speed of the vehicle driven by way of the internal combustion engine lies above a second predetermined threshold value, whether a clutch of the vehicle is engaged, and whether there is not a request from a driver of the vehicle; and if a result of the inquiry is positive, closing the volume control valve for a predetermined period of time; during the period of time, recording values for the fuel pressure by way of the pressure sensor; comparing the values for the fuel pressure with a predetermined threshold value; if the values for the fuel pressure within the time period are below the threshold value sufficiently often, classifying the volume control valve as fault-free; and otherwise classifying the volume control valve as defective.
 2. The method according to claim 1, wherein one of the release conditions is whether the speed of the internal combustion engine lies above the first predetermined threshold value.
 3. The method according to claim 1, wherein one of the release conditions is whether the speed of the vehicle driven by way of the internal combustion engine lies above the second predetermined threshold value.
 4. The method according to claim 1, wherein one of the release conditions is whether the clutch of the vehicle is engaged.
 5. The method according to claim 1, wherein one of the release conditions is whether there is not the request from the driver of the vehicle.
 6. The method according to claim 1, which comprises: selecting the release conditions to include whether the speed of the internal combustion engine lies above the first predetermined threshold value, whether the speed of the vehicle driven by way of the internal combustion engine lies above the second predetermined threshold value, whether the clutch of the vehicle is engaged, and whether there is not the request from the driver of the vehicle; and aborting the diagnosis if, during the time period, at least one of the release conditions is no longer fulfilled.
 7. The method according to claim 1, which comprises aborting the diagnosis if, during the time period, at least one of the release conditions is no longer fulfilled.
 8. The method according to claim 1, which comprises performing the diagnosis once per driving cycle.
 9. The method according to claim 1, which comprises executing the diagnosis at predetermined intervals, provided all activation conditions have been fulfilled for a sufficient length of time.
 10. The method according to claim 1, which comprises, concurrently with closing the volume control valve, briefly opening the pressure control valve for a time shorter than the period of time, and subsequently setting the pressure control valve to a specific hold pressure for a remainder of the period of time.
 11. The method according to claim 1, which comprises experimentally determining the threshold value for the fuel pressure and storing the experimentally determined data in a memory of a control unit.
 12. The method according to claim 2, which comprises experimentally determining the threshold value for the speed of the internal combustion engine and storing the experimentally determined data in a memory of a control unit.
 13. The method according to claim 3, which comprises experimentally determining the threshold value for the speed of the vehicle and storing the experimentally determined data in a memory of a control unit. 